Observation and Modelling of The Upper Atmospheric Density and Winds and Their Dependence on the Geomagnetic Activity.
Prof. Dr. Hermann Lühr
The influence of the Sun on climate is one of the major unknowns in the debate on global warming and on the causes of past climate changes. Although the evidence for solar influence on climate is growing, the origin of the solar variability and the processes by which the variable solar input affects climate change are not well understood. A key parameter related to solar influence on climate is the solar irradiance (i.e. the total flux density of solar energy at the top of the Earth’s atmosphere). The irradiance varies on all timescales on which it has been measured. Unfortunately, the measured time series is too short to draw definite conclusions regarding the influence of these variations on climate. Only with the help of models can sufficiently long time series be constructed, which can serve as a useful input to climate simulations. In this project we follow two paths: Firstly we improve and test models of total and spectral solar irradiance variations during the period of satellite observations. The variations of the spectral output of the Sun have gained additional importance in recent years due to the effect on stratospheric and mesospheric chemistry of the Sun’s UV radiation. Secondly, we use the knowledge gained from the first step to improve the reconstruction of the solar irradiance on the longer term. Here we make use of our recent reconstruction of sunspot number over 11400 years (i.e., the whole holocene or the period of time since the end of the last ice age), which extends our knowledge of this parameter of solar activity by an order of magnitude.